Today, along with dramatic improvements in information processing and telecommunication technologies, demands for network computing techniques for interconnecting computers have been growing simultaneously. These state-of-the-art technologies allow users in remote areas to share computer resources or cooperate smoothly in such work as the sharing, distribution, delivery, and exchanges of information over networks.
There are diverse forms of networks for interconnecting computers. Examples of networks include LANs (local area networks) such as the Ethernet set up to cover limited areas; WANs (wide area networks) each interconnecting LANs using dedicated lines or the like; and the Internet that has grown so large as to interconnect computers on worldwide scale.
The Internet is a globally expanded computer network known as the Network of networks. It started out as a mass of interconnections by servers (mainly UNIX workstations) installed at universities, research institutions and other establishments. Since then more and more servers interconnected with one another, growing eventually into today's colossal network comprising countless servers each disclosing diverse resource objects to countless clients. The servers, known as hosts on the Internet, are usually interconnected as per TCP/IP (Transmission Control Protocol/Internet Protocol).
Over the Internet, numerous services are offered including WWW (World Wide Web), News, TELNET (TELetypewriter NETwork) FTP (File Transfer Protocol), and Gopher.
Of these services, the WWW works as a global information search system providing information spaces in hyperlink structures. The service is deemed the biggest factor that has driven the explosive growth and rapid popularization of the Internet worldwide. As an information search system serving on a global basis, the WWW permits browsing of diverse media including texts, images and sounds in hypertext format. So-called hypertext information handled on the WWW is described in a hypertext format description language known as HTML (Hyper Text Markup Language). At present, countless HTML documents (i.e., information resources) are disclosed on a chargeable basis or free of charge over the Internet. It is common knowledge that under TCP/IP, various information resources including the HTML documents are identified using identifiers in URL (Uniform Resource Locator) form and transferred as per HTTP (Hyper Text Transfer Protocol).
In recent years, high-speed Internet connections over telephone lines (Asymmetric Digital Subscriber Line, or ADSL) and cable TV networks have gained widespread use. The trend has raised expectations for video content distribution services involving motion pictures such as movies, animations, and live broadcasts.
Such content distribution services may be typically implemented by means of so-called streaming technology. The technology coming gradually into general use today is designed to allow audio and video data or the like to be reproduced just as they are being downloaded over the Internet, not waiting for the whole data files to be downloaded preparatory to reproduction. The streaming technology is regarded as the key to next-generation Internet usages. Well-known content distribution systems incorporating the streaming technology include “RealSystem G2” and “Windows Media Technologies.”
There has been proposed a content distribution system wherein a server manages a database covering users authorized to access stored contents so that only the authorized users may receive a stream of the contents.
Another content distribution system has been proposed involves distributing encrypted content data free of charge while access right information specifying the conditions for using the encrypted contents is separately distributed by a server. That is, the system distributes contents while protecting their copyrights with suitable techniques. In response to a request from a client, a right management server distributes access right information bound for the client or its user. The access right information, to be used eventually for billing purposes, includes a user ID or a client ID together with authentication information such as a digital signature of the right management server. The client authenticates the use conditions included in the access right information and, depending on the result of the authentication, decrypts and reproduces encrypted contents using an encryption key sent to the client beforehand or along with the information.
Such content distribution systems as described above allow users to search for and purchase-desired contents from server databases through on-line accounting settling means such as electronic settlements. After completing the legitimate steps of content purchase, the users can access the contents through the client terminals.
Also proposed is a content distribution system whereby contents with their quality reduced in part or as a whole are offered to users on a trial basis subjecting to confirmation of the details of content before purchase. However one disadvantage of this system is that the users must put up with the trouble of searching for desired contents through the large quantities of contents held in databases.
For instance, in the case where one user recommends certain content to another user, another user must search anew for the content in question using an appropriate name or keyword. The content that one user may wish to recommend cannot be explained adequately to any other user unless it is actually reproduced. The elaborative steps involved for content reproduction tend to discourage users from recommending any content to other users under such a system.
There is also the problem of recognition—or the lack of it—in marketing certain contents. Some contents lead brisk business because they are advertised extensively or their authors are well known; other contents barely get the chance to be sold or even recognized because they are buried in huge quantities of themselves.